In U.S. Pat. No. 4,625,993, the contents of which are incorporated herein by reference, there is described a vehicle suspension system comprising wheel suspension devices the displacement of which can be varied, and means responsive to the loading of the suspension devices to feed back to the devices electric signals effecting a predetermined displacement.
In U.S. patent application Ser. No. 747 130 filed on June 4 1985 also by the present inventors and also commonly owned herewith, and of which the contents are again incorporated herein by reference, there is disclosed a wheel suspension device capable of use in such a system and comprising an hydraulic actuator of which the piston position is adjustable in response to forces acting thereon and/or to a selected control input, and a load bearing strut responsive to the actuator piston experience to minimise the load carried by the actuator.
The system of U.S. Pat. No. 4,625,993 offers substantial advantages over previous passive suspension systems, but the full advantages of any such system are obtained only by the input of considerable energy.
It is accordingly an object of the present invention to provide an active vehicle suspension system with reduced energy demand under a wide range of conditions, for a given set of characteristics.
It is also an object of the invention to provide arrangements for the selective damping of the movement of a piston in a cylinder.
It is a further object of the invention to provide a vehicle suspension system including a hydraulic actuator and means for selectively damping movement of the actuator piston due to forces acting thereon.
It is moreover an object of the invention to provide a fluid-pressure actuator operatively associated with fluid pressure means controlled so as to exert a selected positive or negative damping effect on movement of the actuator piston.